Precombustion chamber for diesel engines



Jan. 2, 1940. F. K095 v 2,185,918

PREGOMBUSTION cHAM B ER FOR DIESEL ENGINES Filed March 28, 1938 poprvlezr Patented Jan. 2, 1940 Franz Koch, Essen, Germany ApplicationMarch 28, 1938, Serial No. 198,516 In Germany April 2, 1937 1 Claim.

This invention relates to Diesel engines operating with oils of allkinds, more particularly oils which do not readily ignite, such forinstance as coal tar oils or oils from pressure hydrogenation productsof coals and coal extracts.

Gas oils which are rich in hydrogen and ignite easily can be used in theDiesel engine without any trouble. In many countries which are poor ingas oils, howevemthese oils have to be imported. Whilst the syntheticmanufacture of such easily ignitable Diesel oils which are rich inhydrogen is possible, it is extremely costly. On the other hand, oilswhich are poor in hydrogen, such for instance as oils obtained by thesingle stage 16 hydrogenation of coals, coal extracts and the like arefar cheaper to manufacture. These oils are,

however, just as difficult to ignite as tar oils and cannot be used inmodern Diesel engines, more particularly high speed Diesel engines. Forthis go reason attempts have long been made to render cheap oils of poorquality, for instance coal tar oils and the like, suitable for use inDiesel engines.

It is an essential feature of the Diesel engine,

' that for initiating the ignition of the injected fuel a sufficientlyhigh air temperature must be available at the moment of injection. Thistemperature must be all the higher, themore difficult the fuel beingused is to ignite. Attempts have already been made to ensure theignition of such oils by raising the air temperature beyond thatcorresponding to the compression ratio. For this purpose for instanceincandescent bodies of the most varied construction have been introducedinto Diesel engines. These incandescent bodies have not however been assatisfactory as was expected, as, more particularly at low load and idlerunning and during the starting up of the engine, they could not ensureignition taking place.

The invention overcomes all disadvantages attending the use in Dieselengines of oils which are difficult to ignite, by the provision of aprecombustion chamber having at least one partition memberwhich dividesthe precombustion chamber into a plurality of spaces, said partitionmemher, in addition to being provided with a large central bore locatedin the direction of the fuel jet, being provided at the edge with aplurality of smaller bores, so that only the finest particles at theedge of the jet are held back and ignited while the core of the jet,that is to say the greater part of the fuel, can pass through thecentral bore unhindered. By this means, that portion of the introducedfuel mist at the edge u of the jet is mixed-with the air which passesthrough the 'marginal bores so as to form an ignitable mixture having anoptimum mixture ratio and the ignition being thus made certain. In thehitherto known constructions of Diesel engines the entire quantity ofthe fuel is intro- 6 duced into the combustion space in a more or lessatomised form. In the region of the fuel jet there is thus alwayspresent an excess of fuel and consequently there is no mixture presentof optimum ignitability. Especially started up and when it is runningidle the small quantity of the injected fuel is not properly distributedin the hot air which is present, so that,

in spite of the air temperature being artificially raised, no ignitionwill take place, as the next fuel jet will withdraw too much heat fromthe fuel and air mixture and no ignitable mixture will result.

Examples of Diesel engines illustrating the principle of the inventionare shown in the acl0 companying drawing, in which Fig. l is a sectionthrough 8. Diesel engine of the usual construction with a precombustionchamber, I

Fig. 2 a section through another example of aDiesel engine of theprecombustion chamber type embodying the arrangement according to theintention.

In Fig. 1 the dividing up ofthe jet is effected by a body 3 ofcylindrical form and having a 80 central opening, which is disposed inthe precombustion chamber so as to divide it into an upper space! and alower space 5. According to the size of the central opening 4 and thedistance of the jet separator 3 from the nozzle 2 85 the dividing up ofthe fuel jet can be varied to suit the particular fuel. In theprecombustion chamber Diesel engine illustrated in Fig. 1

over 70% of the fuel was conducted by the jet separator through thecentral opening into the 40 lower space. After the jet separator hadbeen mounted in the precombustion chamber, it was found possible to runthe engine in a perfectly satisfactory manner, even when running idlefor extended periods, with oils which do not ignite readily, forinstance coal tar oils and oils from pressure hydrogenation of coals andcoal extracts with only a small hydrogen content and of a predominantlyaromatic or oleflnic nature. The engine started up just as easily andwith as little trouble as when running on gas oil. Through theinterposition of the jet separator the mixture of the hot air and aportion of the introduced fuel mist was caused to lie in the region ofthe ignitable mixture. Of prime importance for enwhen the engine isbeing 10 suring ignition are with the constructional form illustratedthe size of the central opening of the jet separator and its distancefrom the fuel nozzle.

It thus becomes possible by means of the method according to theinvention to make available for use in Diesel engines the low qualityand cheap oils which do not readily ignite (coal tars and coal tar oilsand the like, also oils from pressure hydrogenation products of coalsand coal extracts and the like) and which hitherto have not beensuitable for use with such engines, owing to the difficulties with theignition.

When the engine is being started up and when it is running idle, that isto say, always when small quantities of fuel are being injected, orwhen, owing to the low speed of revolution of the pump, the atomisationof the injected fuel jet is insuflicient (for instance. with Dieselengines driving vehicles the speed of revolution of the pump variesbetween n=250 and n=1500 revolutions per minute), it has been found thatin many cases it is of advantage'further to subdivide the combustionspace or the precombus tion chamber by disposing several jet separatorsone behind the other. By this means it has been found possible, evenwhen the quantities of injected fuel are small, to ensm-e that in everycase the ignition will be satisfactory and the engine will run'smoothly.The number of the jet separators and their size and the size of thecentral opening differs with different types of engines and the variouskinds of oil and must be determined from one case to another.

In Big. 2, which is a section through a Diesel engine having a cylinderpower of about 25 H. P., although it was possible to. use oils which donot ignite readily, such as coal tar oils and oils from pressurehydrogenation products of coals and coal extracts quite satisfactorilyin all load ranges, smooth running could not be obtained with thisengine. Through the introduction of a second jet separator 8, however,the central opening 1 of which is smaller than the central opening 4 ofthe jet separator 3, it was found possible to overcome all difficultiesand notonly to ensure completely satisfactory running of the engine inall load ranges, but also a smooth and undisturbed operation when theengine is running idle.

Through the introduction of further jet separators it is thus possiblefurther to improve the running of Diesel engines using oils which do notignite readily and which can be used successfully in suchengines throughthe provision of a single jet separator.

What I claim-is: In a Diesel, engine having a main combustion space anda fuel injection nozzle, a precombustion chamber arranged to receive thefuel from said fuel injection nozzle and communicating with the maincombustion space, said precombustion chamber having a plurality ofpartition members arrangedtherein so as to lie in the path of the fueljet from the injection nozzle and divide the precombustion chamber intoa plurality of spaces, each of said partition members having a largecentral aperture located in the path of the fuel jet so as to allow thegreater part of the fuel to pass unhindered to the other side of thepartition member, the central aperture in each successive partitionmember being of smaller diameter than that of the central aperture ofthe partition member nearer the fuel nozzle, so as to hold backprogressively larger quantities of fuel particles at the edge of thefuel jet, said partition members having a plurality of smaller aperturesin the marginal regions thereof for admitting air to said fuelparticles, so as to form therewith a series of ignitible mixtin-eschamber in the precombustion FRANZ KOCH.

